Method of forming recessed socket contacts

ABSTRACT

In a socket used to house semiconductor die during testing, a recessed socket contact is provided that avoids pinching the die&#39;s contacts and allows for smaller socket holes and therefore denser arrays of contacts. In one embodiment, semiconductor fabrication techniques are used to construct a dense array of contacts and the contacts are singulated while maintaining their alignment within the array. A metal layer may be added to the tips of the contacts for better conductivity.

RELATED APPLICATION

This application is a divisional of application Ser. No. 09/265,906,filed Mar. 10, 1999.

TECHNICAL FIELD

The present invention relates generally to devices and methods forproviding electrical connection between two electronic components. Morespecifically, the present invention relates to a socket contactconfigured to establish electrical communication between a semiconductordie and a test device as well as methods for forming the socket contact.

BACKGROUND OF THE INVENTION

Testing a semiconductor die often involves establishing an electricalconnection between testing equipment and the circuitry of a die. Testingmay be performed on an unpackaged die that has been singulated from asemiconductor wafer, on a section of dies that are still part of thewafer, or on all of the dies on a wafer. Moreover, a bare die that hasundergone packaging steps may also be tested. One example of such a dieis a “flip chip,” wherein conductive material such as solder balls areattached directly to the bond pads or electrical traces formed in thesurface of the die; the die is then “flipped,” or mounted face down, sothat the solder balls may connect with contact members of anotherdevice. Another example is a “chip scale package,” which includes a diealong with one or more package elements, such as encapsulating materialin the form of thin protective coatings formed of glass or othermaterials bonded to the face and backside of the die; in addition,solder balls may be attached to electrical traces in the surface of thedie or directly to the die's bond pads through openings in theencapsulating material. A Ball Grid Array (BGA) serves as yet anotherexample that involves even more packaging: the die is wire bonded to thetop of a substrate, encapsulated, and solder balls are bonded toelectrical traces at the bottom of the substrate that lead to thewirebonds.

The device to be tested will hereinafter be referred to as an integratedcircuit chip, or IC chip, regardless of the singulation or packagingstate of the die that forms all or part of the IC chip. One method oftesting the IC chip involves placing the chip into a socket, whichcomprises a body with holes that span through the body. These holeshouse contacts that are aligned with electrical contact points of the ICchip. For purposes of explanation only, it will be assumed that thecontact points of the IC chip are solder balls. Often, the socketincludes a lid that, when closed, pushes the solder balls of the IC chipagainst the heads of the socket's contacts. Once the IC chip has beeninserted, the socket is then plugged into a printed circuit board (PCB).This insertion often involves a biasing force in the opposite directionof the lid's pushing force. To ensure electrical communication betweenthe IC chip and the PCB without the risk of breaking the socketcontacts, the socket contacts are configured to be resilient to thecompression resulting from these forces. One such configuration fordoing so involves the use of “pogo pin” contacts. A pogo pin cancomprise an electrically conductive inner shaft, an electricallyconductive outer shell concentric to the shaft and defining the head ofthe contact, and an electrically conductive spring between the innershaft and outer shell. When the pogo pin undergoes compression, theinner shaft is pushed into the outer shell despite the spring's bias.Ideally, signals received at the head of the outer shell will conductthrough the spring to the inner shaft and onward to devices that may beconnected to the inner shaft. However, such a design allows for unneededelectrical communication along the entire surface of the outer shell.

As an alternate configuration, buckle beams may be used. Buckle beamsare essentially a thin, somewhat rigid length of conductive materialthat will buckle in response to compression from the IC chip and the PCBbeing pushed toward each other. The problem with buckle beams is thatthe holes housing the beams must be wide enough to accommodate thehorizontal motion of the beams as they buckle. The buckling spacerequired limits the density of beams per unit area that can be achieved.In addition, buckle beams tend to rotate during buckling. Thus, incertain aspects, pogo pins and buckle beams run contrary to the needs inthe art for electrical contacts that require minimal space and material.

Returning to the testing process, the PCB with the connected socket isplaced in a chamber, wherein the IC chips are tested while subjected toan elevated temperature. Such testing is referred to as burn-in testing.The socket's contacts provide electrical communication between the ICchip and signals sent through the PCB from the test equipment. Once thetest is complete, the chip is removed from the socket. IC chips which donot pass the testing are discarded, and chips that pass may undergofurther testing and ultimately be used as components in electronicdevices.

Further testing and use of these chips, however, depends upon theability of the solder balls to continue to function after theirinteraction with the socket's contacts. Prior art socket contacts haveheads that are configured through their flexibility to actively exert aforce against the chip's solder balls, wherein the force is generallytransverse to the biasing force that pushes the chip into the socket.The effect of this transverse force is to pinch the solder balls,thereby severely damaging them and making further communication with thechip difficult. Such socket contacts include the aptly named “pinchcontact” found in the Series 655 OTBGA Burn-in/Test Socket sold by WellsElectronics. Another series 655 OTBGA Socket by Wells uses a Y-shapedcontact. The Y-shaped contact is further described in U.S. Pat. No.5,545,050, by Sato et al., indicating that the head of the Y-shapedcontact is flexible, which allows it to “snugly” accommodate ahemispherical conductor of an IC package. (Sato at col. 4, ln. 25-30.)Thus, the Y-shaped contact continues the tradition of applying apinching action to the electrical contacts of a device.

Still other examples of contact heads are illustrated by references fromInterconnect Devices, Inc. (IDI). Among the examples are plunger probetips having crown-shaped heads, whose sharp prongs tend to gouge thesurface of the chip's contact, be it a solder ball or flat pad. Inaddition, IDI discloses a concave tip that might accommodatehemispherical chip contacts such as solder balls, but may provideinsufficient electrical communication for other contacts, such as thoseconfigured as flat pads.

Thus, in addition to the needs in the art discussed above concerning thebody of an electrical connector, there is also a need in the art for anelectrical connector having a head that reduces the damage to theelectrical contacts of IC chips during connection and is configured toaccommodate more than one type and size of chip contact. Morespecifically, there is a need in the art for a socket contact thatminimizes the damage to various IC chip contacts during IC chip testing.

SUMMARY OF THE INVENTION

Accordingly, the current invention provides electrical contacts as wellas methods for forming them. One preferred embodiment comprises acontact as part of a socket used for testing a semiconductor die,wherein the contact has a head that defines a recess, and the head iscoupled to an elongated conductive body configured to fit within asocket. More specifically, the head comprises a portion defining theperimeter of the head, with other portions of the head lower than theperimeter. In one exemplary embodiment, this head takes the form of aplanar ring with a sidewall sloping downward from the ring toward thecentral axis running the length of the contact. This sidewalltransitions to a generally planar section that is parallel to, yet lowerthan, the perimeter ring. Various preferred embodiments address varyingdegrees of transition and planarity of the portions of the contact head.

Other preferred embodiments address the body of an electrical contact,including one embodiment comprising a head, a shaft, and a springcoupling head to the shaft. In a more specific embodiment, the spring'scoils define circles of differing circumferences. Another exemplarypreferred embodiment comprises a metallic tube for the contact body,wherein the tube defines at least one slit. Yet other preferredexemplary embodiments address silicon contacts and methods for formingthem. Specifically, semiconductor fabrication techniques are used todefine an array of silicon contacts, and the contacts are singulatedwhile maintaining their alignment within the array.

Still other preferred embodiments include the recessed contact head asdescribed above in combination with the contact bodies just described.These embodiments include methods and devices wherein the head is formedseparately from the body and attached thereto, as well as methods anddevices wherein the head is integral to the body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of one exemplary embodiment of thecurrent invention.

FIG. 2 is a close-up view of a portion of FIG. 1.

FIG. 3 is a top-down view of the illustration in FIG. 2.

FIGS. 4A and 4B are top-down views of a second and third exemplaryembodiment of the current invention.

FIGS. 5A and 5B are cross-sectional views of fourth and fifth exemplaryembodiments of the current invention.

FIGS. 6A-6D are cross-sectional views of sixth, seventh, eighth, andninth exemplary embodiments of the current invention.

FIG. 7 is a cross-sectional view of a tenth exemplary embodiment of thecurrent invention.

FIG. 8 is a cross-sectional view of an eleventh exemplary embodiment ofthe current invention.

FIG. 9 is a cross-sectional view of a twelfth exemplary embodiment ofthe current invention.

FIG. 10 is a cross-sectional view of a thirteenth exemplary embodimentof the current invention.

FIG. 11 is a cross-sectional view of a fourteenth exemplary embodimentof the current invention.

FIGS. 12A-E are cross-sectional views of an additional exemplaryembodiments of the current invention.

FIGS. 13A-13H illustrate steps of another exemplary embodiment of thecurrent invention.

FIGS. 14A-14C depict alternate steps of yet another exemplary embodimentof the current invention.

FIGS. 15A-15C illustrate alternate steps of still another exemplaryembodiment of the current invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 depicts one exemplary embodiment of the current invention in thecontext of testing an IC chip. IC chip 20, which could be a bare die, aflip chip, a chip scale package, or a die at any stage of packaging, isenclosed within a socket 22. The socket 22 comprises a body 24 made ofelectrically non-conductive material as well as a holding mechanism 26for biasing the IC chip 20 against the body 24. In this particularexample, the holding mechanism 26 is a pair of hinged lids, but thoseskilled in the art know that there are many ways to position the IC chip20. In this position, the IC chip's contacts 28, which are assumed to besolder balls for purposes of explanation, are aligned with holes 30extending in generally one direction through the body 24. Socketcontacts 32 extend through these holes 30 and electrically connect thechip's contacts 28 and the PCB 34. Each socket contact body 36, depictedin an exemplary generic form in FIG. 1, is configured to be resilientalong an axis defined by the biasing force that pushes the PCB 34against the socket contacts 32. This axis is often referred to as the“z-axis” and is further described below. Such resiliency can be achievedthrough known methods, such as with pogo pins or buckle beams, orthrough embodiments of the current invention which will be describedbelow.

The head 38 of each socket contact 32 is configured to receive a chipcontact 28. Contrary to the prior art contacts which have heads in theform of spears, chisels, needles, crowns, or pinchers, exemplaryembodiments of the current invention include socket contacts havingheads that define grooves or recesses or cavities or cups. FIG. 2, forexample, is a close up of the socket contact head 38 depicted in FIG. 1.In this cross-sectional view, one can see that the socket contact head38 comprises a first portion 40 defining a plane 41 and an opening. Inthis embodiment, the plane 41 is parallel to the IC chip 20 positionedwithin the socket 22. Similarly, a second portion 42 is parallel toplane 41 and is lower than the first portion 40, or at least fartheraway from the positioned IC chip 20. Joining the first portion 40 andthe second portion 42 is a third portion 44. In this exemplaryembodiment, the third portion 44 defines a frustum-shaped orfrustoconical wall that slopes toward the center of the socket contact32 from the first portion 40 to the second portion 42. In doing so, thissocket contact head 38 offers a continuous contact region along anentire cross-sectional circumference C of the chip's contact 28. Thiscan be seen better in the top-down view of FIG. 3. Without limiting theinvention, it is believed that by providing such a continuous contactregion, any force biasing the chip contact 28 and the socket contact 32toward each other is distributed, thereby helping to maintain theintegrity of the chip contact 28. It is possible that the compressiveforce applied to the chip contact 28 may be enough to deform it. In thatcase, the chip contact 28 may flatten against the third portion 44 andperhaps against the second portion 42 as well. This would serve toincrease the contact region without inflicting the damage that prior artcontacts would cause with their sharp pikes and corners. It should befurther noted that, in this embodiment and from this viewpoint, thefirst portion 40 is annular, or ring-shaped.

Despite the benefits from the area of connection offered by theexemplary embodiment above, it may not be necessary to provideconnection along the entire circumference C. Accordingly, the currentinvention includes within its scope electrical connectors having headsthat define polygons in a top-down view. FIG. 4A, for example,illustrates a socket contact head 138 comprising a triangular firstportion 140, second portion 142, and third portion 144. Assuming thechip contact 28 is still a semi-spherical solder ball, then electricalconnection may occur at three points P1, P2, and P3, along a particularcross-sectional circumference C. FIG. 4B depicts yet another socketcontact head 238 having a rectangular first portion 240, second portion242, and third portion 244. Accordingly, electrical connection may occurat four points P4-P7 along a particular cross-sectional circumference C.While the biasing force will be distributed to fewer points in the FIG.4 embodiments in comparison to FIG. 3, it should be noted that thecontact points P1-P3 and P4-P7 occur on planar areas of the socketcontact heads 138 and 238. As a result, deformation of the chip'scontact 28 will be minimal.

In the embodiments discussed above, the socket contact heads 38, 138,and 238 have been sized so that only the third portion 44, 144, or 244is configured to touch the chip contact 28. However, other embodimentsare included wherein the head of the electrical connector is sizeddifferently in relation to the chip's contact. In FIG. 5A, a socketcontact head 338 is sized and shaped to allow for connection not onlyalong the cross-sectional circumference C but also at a point B at thebottom of the chip contact 28. In FIG. 5B, socket contact head 438 issized and shaped to initially touch point B at the bottom of the chipcontact 28. Once again it is possible that some deformation of chipcontact 28 will occur as it is pressed against socket contact head 438,thereby increasing the area of contact. However, since chip contact 28is abutting a generally flat plane 442, deformation will not be asdamaging as it would be with prior art socket contact heads.

As shown in FIG. 6A, a socket contact head 538 can also be sized so thatthe chip contact 28 touches the socket contact head 538 where the firstportion 540 and third portion 544 meet. In the FIG. 6A embodiment, thearea where these two portions 540 and 544 meet defines a corner 500. Asa result, it may be desirable in certain embodiments to provide a morerounded area 600, as seen in FIG. 6B, representing the transition fromthe first portion 640 to the third portion 644 of socket contact head638. Further, FIG. 6C's embodiment demonstrates that it may bebeneficial in some embodiments to include an area 700 providing a moregradual or rounded transition from the third portion 744 to the secondportion 742. Moreover, it is not required in some embodiments that thefirst and second portion be planar. The socket contact head 838 in FIG.6D comprises a first portion 840 that curves outward in a convexmanner—toward the positioned IC chip 20 and its contact 28. On the otherhand, the second portion 842 and third portion 844 curve inward in aconcave fashion—away from the positioned IC chip 20 and its contact 28.As a result, the portions 840, 842, and 844 define a contact surface 800that is generally if not completely complimentary to the shape of thechip contact 28. Specifically, the curved shape of surface 800corresponds to the curved shape of the chip contact 28.

However, it may be helpful in some embodiments to maintain the planarityof at least the first portion 40. FIG. 7 depicts the socket contact head38 depicted in FIG. 2 with a different chip contact 928. In this case,chip contact 928 is planar, as may be found in Land Grid Array (LGA)packages. In LGA packages, a plurality (array) of contact pads (“lands”)are used to communicate with the packaged die circuitry. As ispreferred, the planar first portion 40 of the socket contact head 38corresponds to the planar chip contact 928.

In the embodiments described above, it is noted that the contact head'sperimeter—or portion of the contact head that is outermost from thecentral longitudinal axis of the contact—is also the “highest” area ofthe head or farthest from the body of the contact. In certaincircumstances, the outermost portion could also be described as beingclosest to the site in which the contact of an IC chip will occupy whilebeing housed in the socket. In addition, because the remainder of thehead declines and/or converges toward the central longitudinal axis,these exemplary embodiments can be considered to be defining a centralor inner recess or cavity.

In many embodiments, an electrical connector head such as the socketcontact heads described above is preferably made of an electricallyconductive material. More preferably, the embodiments are made of metal.Exemplary materials for the electrical connector head include gold,copper, beryllium copper, and stainless steel. The shape of theelectrical connector head may be formed through chemical etchingtechniques—including wet or dry (plasma) etching—or through stamping.Further, the head may be integral to the body of the electricalconnector or may be a discrete part that is attached to the body. Forexample, it is possible to shape the head by die-stamping a metal sheet,then attaching the completed head to an electrical connector body usinga conductive adhesive, such as a Silva-based material (Silva FilledConductive Chip Adhesive is a conductive ink composed of silver flakesin an epoxy base which can be purchased from Ablestick Laboratories ofGardena, Calif.). In some exemplary embodiments, it is preferable tochoose a metal type and thickness so that flexibility in the head, ifany, does not result in any pinching action against the chip contactupon biasing the IC chip and socket contact against each other.

As stated above, the electrical contact head may be associated with anelectrical contact body that is already known in the art. In the contextof socket contacts, for example, FIG. 8 illustrates the socket contacthead 38 as part of a pogo pin 46. The socket contact head 38 isconnected to, if not an integral part of, an outer shell 48. The socketcontact head 38 is also connected to an inner shaft 50 through a spring52. However, if the outer shell 48 is made of an electrically conductivematerial, then the entire shell 48 is available to receive current, whenall that is really needed is for current to travel from the head 38 tothe shaft 50 through the spring 52 (as well as in the reversedirection). In addition, the hole 30 must be wide enough to accommodatethe diameter of the shell 48. As technology allows for small chipcontacts 28 that may then be more closely packed together, it isdesirable to densify the socket holes 30 in a corresponding manner. Theadditional width needed for the outer shell 48 runs counter to thatdesire.

Accordingly, the current invention includes electrical contacts thatdispense with an outer shell. As one example, FIG. 9 depicts a socketcontact 1032 comprising a socket contact head 38 coupled to a shaft 1050through a spring 1052. The spring 1052, in turn, has sections definingvarying widths. For instance, spring 1052 comprises a first section 54and second section 58, whose coils define a circle having a diameter ofabout 1 mil; as well as a third section 56 having coils that define acircle having a diameter of about two mils. The third section 56 is wideenough to contact the socket's body 24. The absence of an outer shellallows for a narrower hole 30 and therefore allows for a denser array ofholes 30 in the socket body 24.

Another electrical contact body that is known in the art is the bucklebeam, and the current invention includes electrical contact heads suchas the ones described above attached to such a body. However, to avoidthe problems associated with buckle beams, the current invention alsoincludes within its scope embodiments such as the one in FIG. 10,wherein a socket contact 1132 comprises a socket contact head 38 and atube 60 having at least one aperture 62. Thus, when a compressive forceis applied to the socket contact 1132, at lease some of that force willcause the tube 60 to collapse in on itself, initiating the closure ofthe aperture 62, rather than cause the tube 60 to buckle laterally.Thus, hole 30 need not be as large as when it accommodates buckle beams.The tube is nevertheless resilient enough to generally return to itspre-compression shape once the compressive force eases. Further, thetube 60 is configured to fit snugly against the socket body 24 somewherealong its length. Other embodiments have a plurality of apertures, suchas FIG. 11, wherein two apertures, 62 and 64, appear at the same depthbut on different sides of the tube 60. FIG. 12A depicts two apertures,62 and 66, at different depths along the tube 60. The tube 60 in theseand other embodiments are preferably made of metal such as gold, copper,beryllium copper, or stainless steel. The aperture or apertures can beformed by sawing. In addition, since it is also preferred to make thesocket contact head from metal, it is possible to form the head 38 andtube 60 from the same piece of metal.

Still other embodiments include other contacts with bodies defining agenerally continuous profile but for at least one deformation ordeviation. For example, apertures of different shapes may be formed.While the contacts in FIGS. 10, 11, and 12A define a rectangular profilewith a deformation in the form of a second, smaller rectangle (or aslit), it is possible to define a different deformation by using adifferent saw blade, by using a particular etching technique, or simplyby stamping a dent into the contact body. FIG. 12B exemplifies such adifferent deformation—in this case a semi-circular deformation 62′ isdefined from a body 60′ having a generally rectangular profile definedby body's cylindrical shape. Moreover, the contact body in theembodiments described above, as well as others, can be hollow. Methodsfor making such a hollow body can be similar to those known in the artfor making the outer shell 48 of the pogo pin depicted in FIG. 8. Ahollow body allows embodiments such as the one depicted in FIG. 12C,wherein metal strips 64′ and 66′ integrally extend from and joincylindrical portions of the contact body 60′. That embodiment can beformed by sawing on opposite ends of the hollow body, as depicted inFIG. 12D. FIG. 12D is a top-down cross sectional view of the contact inFIG. 12C. Saw blades 68′ move in the direction indicated by arrows 70′,thereby defining strips 64′ and 66′ from the cylindrical shell body 60′.Saw blades 68′ can represent two blades that saw the body 60′simultaneously or one saw blade that saws the body 60′ at differentplaces and at different times. FIG. 12E is another side view of thisembodiment, similar to FIG. 12C, only at a slightly different angle thanthat of FIG. 12C. In FIG. 12E, the strip 64′ is closer to the viewerthan strip 66′. In response to a compressive force along the length ofthe contact body 60′, the strips 64′ and 66′ can buckle, allowing thebody 60′ to at least partially close the gap 72′. In yet anotherembodiment, seen in FIG. 12F, the strips 64′ and 66′ may be deformed or“predented” through stamping or other methods, to encourage an inwardcollapse in response to compression. Once again, these embodiments canreturn to their shape as the compression eases.

While all-metal electrical contacts are preferable in terms ofelectrical conductivity, it may sometimes be preferable to usesemiconductive materials for at least the body of the electricalcontact, as this allows for the use of fabrication techniques thatsupport scaling on par with the techniques used to define the contactpitch in the IC chip that is to be tested. FIGS. 13A through 13Hdemonstrate such fabrication techniques that may be used in embodimentsof the current invention to form an electrical contact. FIG. 13A shows asemiconductor substrate 68 that has been patterned on the top and bottomwith photoresist 70 so as to define a plurality of contact bodies. Forpurposes of explanation, it is assumed that the substrate is made ofsilicon that has been doped to encourage electrical conductivity. Next,as seen in FIG. 13B, the shape of the top and bottom of the in-processcontact bodies are defined through etching. FIG. 13B indicates that anahisotropic etch has been performed on the top and bottom. The fact thatplateaus 72 remain on the bottom suggests that the anisotropic etch onthe bottom was either shorter in time or involved a lower etch rate thanthe anisotropic etch on the top; or that the openings defined by thephotoresist on the bottom were larger than the openings on top.Partially defining the contacts also establishes the placement of eachprospective contact relative to the other prospective contacts. Anysilicon remaining between the designated contact sites continues todetermine the alignment of each contact in the array of contacts untilthat silicon is replaced with another material. Such a step isillustrated in FIG. 13C, where the photoresist is removed and theposition of each in-process contact is maintained relative to the otherin-process contacts, in this case through the application of a z-axiselastomer 74 to the bottom of the substrate. The z-axis elastomer 74 isan adhesive material that is capable of conducting electricity along adimension in response to pressure applied along that dimension. Thedirection of pressure is usually designated as being aligned with az-axis, wherein the elastomer sheet is generally parallel to a planedefined by an x and y axis (and wherein the x, y, and z axes are 90°from each other). Such an elastomer is generally nonconductive along thex and y axes.

Once the alignment of the in-process contacts has been reinforced, thecontacts are then singulated by removing the remaining siliconinterconnecting the in-process contacts. One option for doing so isshown in FIG. 13D, wherein additional photoresist 76 is patterned toprotect the tops of the in-process contacts, and the substrate 68subsequently undergoes an isotropic etch to form the sidewalls of thein-process contacts. Preferably, the isotropic etch is continued tocompletely separate the contacts 1232, as depicted in FIG. 13D.Alternatively, the isotropic etch may be used to partially define thesidewalls (FIG. 13E), with an anisotropic etch completing thesingulation (FIG. 13F). Once the additional photoresist 76 has beenremoved, FIG. 13G shows that the array of discrete contacts 1232, alongwith the z-axis elastomer 74 maintaining their placement, may then bemoved to a substrate 78 such as a PCB having conductive leads 80 thatend under the contacts 1232. When the contacts 1232 undergo compression,the z-axis elastomer 74 provides resiliency as well as electricalcommunication between the contacts 1232 and the leads 80. It may also bedesirable in some embodiments to deposit insulation 82 between thecontacts 1232 for added stability. This can be accomplished with ablanket deposition of an insulating layer followed by an etchback, withphotoresist protecting the contacts. The end result is the socket 1322illustrated in FIG. 13H. As with previous sockets, an IC chip's contactswill connect with the socket's contacts 1232, and the PCB's conductiveleads 80 can be wire bonded to test equipment for testing the IC chip.

Variations of the processes described above also fall within the scopeof the current invention. For example, sidewall definition andsingulation of the contacts can be accomplished with a saw such as thoseused to singulate dice from a wafer. In addition, there are ways toretain the alignment of the contacts 1232 other than using the z-axiselastomer 74. For example, after the step illustrated in FIG. 13B, analternate step shown in FIG. 14A may be taken. That figure illustratesthat the photoresist 70 has been removed and another layer of resist 84has been applied and patterned to protect the tips of the in-processcontacts. FIG. 14A further indicates that the sidewalls of thein-process contacts have been defined, either through etching or sawing.Subsequently, the insulation layer 82 is provided to a desired height,and the resist 84 is removed (FIG. 14B). In this embodiment, it is theinsulation layer 82 that maintains the alignment of the in-processcontacts. Singulation may then be completed by etching or sawing fromthe bottom of the substrate 68, the result of which is seen in FIG. 14C.The z-axis elastomer 74 may still be used, but in this embodiment, itmay be initially deposited on the substrate 78, with the singulatedcontacts 1232 and insulation 82 being placed thereover.

In addition, a metallization step may be added to make the tip of thecontacts 1232 more electrically conductive. Moreover, it should be notedthat the tip of the contacts may be formed in accordance with theconfigurations described above for providing a contact head with agroove or recess or cavity or defining a cup shape, with the v-shapedrecesses depicted in the contacts 1232 of FIGS. 13H and 14C serving asone example. As another example, the etch time, etch rate, or resistopening could be established, as is known in the art, to define acontact tip that more closely resembles the socket contact head of FIG.2. The result of such a step appears in FIG. 15A. A metal layer couldthen be provided and subsequently patterned using photoresist to defineheads 1438 of the in-process contacts. Additional steps as illustratedin FIGS. 13C-13H may be performed to reach the result depicted in FIG.15C, wherein each contact 1232 has a metallic head 1438 comprising afirst portion 1540 defining a plane 1541 and an opening. In thisembodiment, the plane 1541 is parallel to the substrate 78. Similarly, asecond portion 1542 is parallel to plane 1541 and is lower than thefirst portion 1540, or at least closer to the substrate 78. Joining thefirst portion 1540 and the second portion 1542 is a third portion 1544.In this exemplary embodiment, the third portion 1544 defines afrustum-shaped or frustoconical wall that slopes in toward center of thesocket contact 1232 from the first portion 1540 to the second portion1542. As an alternative to using a metallization step, it is also withinthe scope of the current invention to form a metal head separately andattach it to a silicon contact.

One skilled in the art can appreciate that, although specificembodiments of this invention have been described for purposes ofillustration, various modifications can be made without departing fromthe spirit and scope of the invention. For example, just as embodimentsconcerning a socket contact head may be associated with prior art socketcontact bodies, so too can embodiments of socket bodies be used inconjunction with prior art socket heads. Moreover, concerningembodiments involving the testing of electronic devices, the devices andmethods covered by the current invention could be used in testsincluding burn-in, connectivity checks, open short tests, and multichipmodule tests, as well as others. As for embodiments addressing which ICchips could be tested, the current invention includes embodiments thatinvolve testing packages such as dual in-line (DIP), zig-zag in-line(ZIP), leadless chip carrier (LCC), small outline package (SOP), thinsmall outline package (TSOP), quad flat pack (QFP), small outline j-bend(SOJ), and pin grid array (PGA) packages in addition to the bare die,chip scale package, flip chip, BGA, and LGA mentioned above. Moreover,the methods and devices described above are not limited to testingcircumstances; rather, they could also be used for interconnect devicesin permanent or semi-permanent packaging. Accordingly, the invention isnot limited except as stated in the claims.

What is claimed is:
 1. A method of forming an electrical contact,comprising: providing a planar doped silicon substrate having a top anda bottom surface patterned to define a plurality of contact bodies;partially forming an electrical contact by etching the top and thebottom of the substrate; forming an electrical contact surface from thetop surface of the substrate; depositing a metallic layer over theelectrical contact surface of the substrate; patterning a contact headfrom the metallic layer; and forming a discrete electrical contact bodyfrom the metallic layer and the contact head.
 2. The method in claim 1,wherein forming an electrical contact surface comprises: anisotropicallyetching a cavity from the top surface of the substrate; and protecting afirst portion of the substrate from the etching.
 3. The method in claim2, wherein forming an electrical contact surface further comprisesretaining a planar second portion of the substrate under the cavity. 4.The method in claim 3, wherein patterning a contact head from themetallic layer comprises: protecting a section of the metallic layeroverlying the first portion of the substrate, an anisotropically etchedportion of the substrate, and the second portion of the substrate withan etch resistant material; and etching an unprotected section of themetallic layer.